Stainless steel members, after being forged or rolled into a predetermined shape, are commonly subjected to heat treatments such as solution treatment.
For example, Japanese Unexamined Patent Application Publication No. 2012-140690A discloses technology of heat treating a stainless steel member, wherein the stainless steel member is forged at high temperatures from 1000 to 1300° C., cooled, and then heated again at high temperatures from 950 to 1125° C. This technology comprises rapidly cooling the stainless steel member after heating at a cooling rate of 5 to 4° C./min.
In addition to the technology described in Japanese Unexamined Patent Application Publication No. 2012-140690A, the technology described in Japanese Unexamined Patent Application Publication No. 2007-146204A is also technology related to the present invention. This technology relates to heat treating an aluminum alloy member, wherein the aluminum alloy member is heated, then rapidly cooled by a cooling medium sprayed from a plurality of nozzles. When a metal member is rapidly cooled, due to the shape of the metal member, some portions tend to cool faster than other portions and some portions tend to cool slower. Thus, high and low temperature portions are created within the metal member. Consequently, at the cooling stage of the metal member, thermal stress and strain are caused in the metal member. In light of this, the technology described in Japanese Unexamined Patent Application Publication No. 2007-146204A comprises adjusting the amount of cooling medium sprayed from the plurality of nozzles to minimize or prevent strain caused in the aluminum alloy member at the rapid cooling stage.